The First Council of Nicaea (325) established two rules, independence of the Jewish calendar and worldwide uniformity, which were the only rules for Easter explicitly laid down by the Council.
(See also Computus and Reform of the date of Easter.) In particular, the Council did not decree that Easter must fall on Sunday. The following day, Easter Monday, is a legal holiday in many countries with predominantly Christian traditions.
Easter therefore varies between 4 April and 8 May in the Gregorian calendar (the Julian calendar is no longer used as the civil calendar of the countries where Eastern Christian traditions predominate).
Also, because the Julian "full moon" is always several days after the astronomical full moon, the eastern Easter is often later, relative to the visible moon's phases, than western Easter.
Easter and the holidays that are related to it are moveable feasts which do not fall on a fixed date in the Gregorian or Julian calendars which follow only the cycle of the sun; rather, its date is determined on a lunisolar calendar similar to the Hebrew calendar.
Christ is flanked by saints, and Satan—depicted as an old man—is bound and chained.
Easter is linked to the Jewish Passover by much of its symbolism, as well as by its position in the calendar.